÷_÷

i dont remember if it stated if she was an adult or a teenager but i feel like being in a baby's body and environment would probably regress certain habits. she does have some deep thoughts such as debatin whether to tell the truth or not or like reasoning/understanding other kids emotions a bit even if shes not always right (i mean lots of adults still are bad at this). i feel like shes got the brain of a 12-13 yr old and she just acts cute cuz thats how a 3yr old should be lol

I read somewhere in a chapter, she's got brain glitch when she wants to act adult like but she went crying like a baby instead.

I think even when she's mentally an adult, her mental adapted to her baby's body

if you just want a scientific reason, it's probably because even though her soul is a teen/adult, her body is a child; and so her brain is still in development/growing stages.
For example, for the same reason your brain degenerates and becomes forgetful, just on the opposite spectrum...

But I don't think i'll give the author that much credit LOL.

Honestly this feels more real than other webtoons where the children act freakishly grown af

Lady Baby? XD
Ig i kinda agree